Female protein is a sex limited serum protein of Syrian hamsters and is homologous to human C-reactive protein (CRP) and amyloid P component (AP). CRP and AP are related members of the pentraxin family of proteins, but have separate functional capacities. FP appears to express certain functional attributes of both CRP and AP. Thus, although structurally more similar to AP, FP has been shown to bind PC similar to CRP. Now it is apparent that FP can bind C1Q and activate complement similar to CRP. On the other hand, FP also has been shown to be a component of hamster amyloid and, therefore, functionally mimics the AP-amyloid relationship seen in human and experimental amyloid. Furthermore, serum FP and amyloid FP are not sequestered populations but appear to exist in a state of dynamic equilibrium.